TAB semiconductor devices are usually downset using a mechanical pushing action. This is either performed on a gang Inner Lead Bond (ILB) machine, immediately after bond, or as a secondary operation on a special purpose tool.
The object of the downset operation is to lift the TAB leads away from the edge of the semiconductor die. If downset is not performed, the leads may tough the die edge, causing short circuits or leakage. Precise control over the downset operation is critical, as too little downset may not lift all leads sufficiently. Too much downset may induce stresses, causing weakness in the leads, and potential lead failure.
Prior art methods for downset on an Inner Lead Bonder has used a thermode to push down the die. This method lowers and bonds the tape to the die. The bond stage then lowers a controlled distance, and the thermode follows down to downset the tape while the tape remains clamped in place. In this method, the thermode and stage must be designed to allow downset, and must be capable of accurately controlled movement. Sizing of the thermode is critical. To get ideal downset, the thermode must be sized equal to bump dimensions. This makes alignment of the thermode to tape and die very difficult.
Another method is to push the die down after bonding, using a precisely sized plunger to prevent uneven downset. In this method the tip of the plunger presses the delicate surface of the die, and any imperfections in the face of the plunger, or trapped particles may cause damage to the die. Keeping the die level during downset is difficult, as the two have to be exactly centered on the die.
The technical advance represented by the invention as well as the objects thereof will become apparent from the following description of a preferred embodiment of the invention when considered in conjunction with the accompanying drawings, and the novel features set forth in the appended claims.